OPEC may cut its oil production for the first time in five years.

OPEC could be forced to reduce its oil production by half a million barrels a day when it meets in December, the first cut in five years, as the latest forecasts show the U.S. shale boom will dent demand for its crude next year, Gulf delegates within the group said.

Oil markets are brimming with new barrels coming out of U.S. shale reservoirs, and separate forecasts from the Organization of the Petroleum Exporting Countries and the...